The present invention relates to a dispersion liquid composition being used for preparation of black matrix of a display surface of a display device such as a cathode ray tube, or similar device. In addition, the present invention relates to a display device such as a cathode ray tube, a plasma display panel (PDPs) and a field emission display (FED), and manufacturing method thereof.
In general, on an interior surface of a glass panel of a faceplate of a color cathode ray tube, a blue-emitting phosphor layer, green-emitting phosphor layer and red-emitting phosphor layer are disposed in dots or in stripes. By impinging an electron beam on the respective phosphor layers, the respective phosphors emit the respective colors to result in display of images.
On such a display surface of a color cathode ray tube, to enhance contrast through absorption of light from other than the respective phosphors, among phosphor dots or phosphor stripes that form adjacent pixels, a light absorption layer (black layer) is disposed as black matrix. Formation of the light absorption layer is performed, for example, in the following way. On an interior surface of a glass panel, photo-resist is coated, the coated photo-resist layer is exposed to a ultra-violet light beam through a shadow mask, and the exposed photo-resist layer is developed to form a resist pattern consisting of dots or stripes. Thereafter, thereon a dispersion liquid of a light absorptive substance is coated to bind, then with a decomposing agent such as hydrogen peroxide water, the resist layer and the layer of the light absorptive substance formed thereon are dissolved and separated to form the light absorption layer.
As the dispersion liquid of the light absorptive substance, as disclosed in Japanese Patent Application KOKOKU Publication No. 51(1976)-5856, water suspension that contains approximately 10% by weight of fine particles of graphite, approximately 1% by weight of a binder such as water glass, and a dispersing agent such as carboxymethyl cellulose is known.
However, in the display surface thereon the light absorption layer of which main component is graphite is formed, the light absorptive layer suppresses effectively diffusive reflection of ambient light but can not suppress sufficiently specular reflection thereof.
That is, in the light absorption layer that is formed by coating a dispersion liquid including graphite to bind, as shown in FIG. 11A, of light 52 incident from outside of the panel (glass panel) 51, the diffuse reflection light 54 that is approximately homogeneously reflected in all direction at an interface of the panel 51 and the light absorption layer 53 can be effectively reduced. However, as shown in FIG. 11B, the light 55 reflected specularly according to the law of reflection at the interface of the panel 51 and the light absorption layer 53 can not be reduced sufficiently. Accordingly, there was a problem that the ambient light such as fluorescent lamp is added on the display surface to cause a difficulty in observing the display surface.
The present invention is carried out to solve such problems. An object of the present invention is to provide a dispersion liquid composition for black matrix that enables to form a light absorption layer that, in a display surface of a display device such as a cathode ray tube, remarkably reduces reflectivity at the interface between a light absorption layer and a panel to make the ambient light less additive.
In addition, another object of the present invention is to provide a display device of which interface between the light absorption layer that is black matrix and the panel is reduced in reflectivity to make the ambient light less additive, and a manufacturing method thereof.
A first aspect of the present invention relates to a dispersion liquid composition for preparation of black matrix. The dispersion liquid composition comprises manganese oxide of an average particle diameter of 50 to 2000 nm, or solid solution of manganese oxide and ferric oxide of which an average particle diameter is in the range of 50 to 2000 nm and manganese content is in the range of 15 to 70% by weight, at least one kind of dispersing agent selected from a group of water soluble acrylic resin, sodium salt, ammonium salt or potassium salt of water soluble acrylic resin, sodium salt, ammonium salt or potassium salt of polycarboxylic acid or lignin sulfonic acid or bisphenol sulfonic acid, and water or an organic solvent compatible with water, respectively.
A second aspect of the present invention relates to a display device. A display device comprises a transparent panel, a light absorption layer disposed on an interior surface of a panel as black matrix, and phosphor layers disposed on a rear surface side opposing to the panel with respect to the light absorption layer. The light absorption layer contains, as the main component thereof, manganese oxide of an average particle diameter of in the range of 50 to 2000 nm, or solid solution of manganese oxide and ferric oxide of which average particle diameter is in the range of 50 to 2000 nm and manganese content is in the range of 15 to 70% by weight.
A third aspect of the present invention relates to a manufacturing method of the display device. The manufacturing method comprises a step of forming a light absorption layer as black matrix on an interior surface of a transparent panel, and a step of forming phosphor layers on the rear surface side opposing to the panel with respect to the light absorption layer. In the step of forming the light absorption layer, a dispersion liquid is coated on the interior surface of the panel to bind. Here, the dispersion liquid contains manganese oxide of an average particle diameter of in the range of 50 to 2000 nm, or solid solution of manganese oxide and ferric oxide of which average particle diameter is in the range of 50 to 2000 nm and manganese content is in the range of 15 to 70% by weight, at least one kind of dispersing agent selected from a group of water soluble acrylic resin, sodium salt, ammonium salt or potassium salt of water soluble acrylic resin, sodium salt, ammonium salt or potassium salt of polycarboxylic acid or lignin sulfonic acid or bisphenol sulfonic acid, and water or a mixed solvent of water and an organic solvent compatible with water.
In the present invention, as the light absorption substance, manganese oxide of which average particle diameter is controlled in the range of 50 to 2000 nm, or solid solution of manganese oxide and ferric oxide of which average particle diameter is controlled in the range of 50 to 2000 nm is employed. Manganese oxides can be manganese dioxide (MnO2), dimanganese trioxide (Mn2O3), trimanganese tetroxide (Mn3O4), dimanganese heptoxide (Mn2O7), or similar compound. In particular, manganese dioxide is preferably employed.
In addition, manganese oxide or the solid solution of the manganese oxide and ferric oxide having such an average particle diameter is preferably included in the ratio of 0.5 to 60% by weight with respect to the total dispersion liquid, more preferable to be included in the ratio of 5 to 35% by weight. When the content of manganese oxide or the solid solution of manganese oxide and ferric oxide is less than 0.5% by weight of the total dispersion liquid, as the black matrix of the display device such as cathode ray tube, a light absorption layer (black layer) having sufficient light shielding property can be formed with difficulty. On the other hand, when the content exceeds 60% by weight, viscosity of the dispersion liquid becomes too high to coat uniformly on the panel even if an additive that will be described later is added.
Further, as a solid solution of manganese oxide and ferric oxide, one of which manganese content is more than 15% by weight can be employed. In particular, one of which manganese content is in the range of 15 to 70% by weight is preferably employed. The solid solution of which manganese content is less than 15% by weight, as the black matrix of the cathode ray tube or similar, is difficult to form a light absorption layer having sufficient light shielding property. On the other hand, when the manganese content of the solid solution exceeds 70% by weight, lowering effect of specular reflectance and diffuse reflectance becomes approximately equal with manganese oxide, that is, the advantage employing the solid solution with ferric oxide is lost.
By varying the average particle diameter of manganese oxide, and the solid solution of manganese oxide and ferric oxide, dispersion liquids including each of them were prepared, respectively. The prepared dispersion liquids were coated on the glass panels to form light absorption layers. The diffuse reflectance (Rr %) and specular reflectance (Rm %) were measured from the panel side and the results are shown in FIG. 1.
The light absorption layers were formed by coating the dispersion liquids containing 12% by weight of manganese dioxide (MnO2) or solid solution of manganese dioxide and ferric oxide (MnO2.Fe2O3), manganese content of which was 40% by weight, 0.6% by weight of ammonium salt of copolymer of acrylic acid-ethoxytriethyleneglycolmethacrylate, and 87.4% by weight of water, over the whole interior surface of glass panels of light transmittance of 80% with a thickness of 0.5 xcexcm by a spin coat method and by drying them. Then, on this light absorption layer (an undercoat shielding layer), a blue phosphor slurry containing a blue-emitting phosphor (ZnS: Ag, Al) was coated by the spin coat method and dried to form a blue phosphor layer of a thickness of 15 xcexcm.
Further, measurement of the diffuse reflectance (Rr %) and the specular reflectance (Rm %) was carried out by the following way. In the measurement of the diffuse reflectance, as shown in FIG. 2A, a sample panel having a light absorption layer 2 containing manganese dioxide or solid solution of manganese dioxide and ferric oxide on the interior surface of a glass panel 1 was disposed in a dark room with the exterior surface of the panel 1 directed toward an upper direction. Here, from an angle of 45xc2x0 with respect to a normal line 1 established at the center of the panel, light of a fluorescent lamp 3 was irradiated. With a brightness-meter 4 disposed on the normal line 1, brightness of reflected light was measured relative to that of a reference white diffusing plate (reflectance of 99.9%). The measured value was converted into the absolute reflectance to obtain diffuse reflectance.
On the other hand, the measurement of the specular reflectance was performed in the way shown in FIG. 2B. As identical as the case of the diffuse reflectance, a sample panel was disposed in a dark room with the exterior surface of the panel 1 directed toward an upper direction. On this panel, from an angle of 45xc2x0 with respect to a normal line 1 established at the center of the panel, light of a fluorescent lamp 3 was irradiated. The brightness of the reflected light was measured relative to that of the reference white plate by a brightness-meter 4 disposed on the opposite side of irradiation with an angle 45xc2x0 with respect to the normal line 1. The measured value was converted into the absolute reflectance.
Further, with similar sample panels, light transmittances were measured and the results are shown in FIG. 3.
From the results shown in FIG. 1 and FIG. 3, the following is confirmed. That is, when the average particle diameter of MnO2 or MnO2.Fe2O3 in a dispersion liquid exceeds 2000 nm, the specular reflectance (Rm %) of the formed light absorption layer (black layer) increases remarkably. On the contrary, when the average particle diameter of MnO2 or MnO2.Fe2O3 is less than 50 nm, the light transmittance increases remarkably to deteriorate the light shielding property. Since, as a result of this, the emitted light from the phosphor layer goes astray to deteriorate color purity.
Further, when compared the light absorption layer including MnO2 with the light absorption layer including MnO2. Fe2O3 that is solid solution, in the range of an average particle diameter of 2000 nm or less, the latter one is superior to the former from the viewpoint of reduction of the specular reflectance and the diffuse reflectance.
In the dispersion liquid composition of the present invention, in order to disperse homogeneously manganese oxide or solid solution of manganese oxide and ferric oxide having such an average particle diameter in a solvent, and to prevent coagulation from occurring, a dispersing agent is added. As the dispersing agent, at least one kind selected from the group of water-soluble acrylic resins that are polymers or copolymers of acrylic acid, methacrylic acid or their derivatives, sodium salt, ammonium salt or potassium salt of said water-soluble acrylic resin, or sodium salt, ammonium salt or potassiun salt of polycarboxylic acid or lignin sulfonic acid or bisphenol sulfonic acid can be used.
Here, as derivatives of acrylic acid or methacrylic acid that constitute water-soluble acrylic resin, n-butyl methacrylate, benzil methacrylate, 2-phenylethylmethacrylate, ethoxytriethyleneglycolmethacrylate, ethoxyethylmethacrylate, butoxyethylmethacrylate, ethoxytriethylenemethacrylate, methoxypolyethyleneglycolmethacrylate, methylacrylate, ethylmethacrylate, isobutylmethacrylate, 2-ethylhexylmethacrylate, isodecylmethacrylate, n-laurylmethacrylate, tridecylmethacrylate, cyclohexylmethacrylate, 2-hydroxyethylmethacrylate, 2-hydroxypropylmethacrylate, dimethylaminoethylmethacrylate, diethylaminoethylmethacrylate, ethoxydiethyleneglycolacrylate, methoxydiethyleneglycolacrylate, methoxytriethyleneglycolacrylate, methoxydipropyleneglycolacrylate, phenoxyethylacrylate, phenoxypolyethyleneglycolacrylate, 2-hydroxyethylacrylate, 2-hydroxypropylacrylate, 2-acryloyloxyethyl succinic acid, 2-acryloyloxyethyl phtalic acid, 2-acryloyloxyethylhexahydro phtalic acid, 2-hydroxyethylacrylate, 2-hydroxypropylacrylate can be cited. Further, as commercial products of such water-soluble acrylic resins or the salts thereof, POLYFLOW No.90, POLYFLOW WS-30, FLOWLEN TG-730W (all of them are products of Kyoei Chemical Co.), AQUALIC HL-415 (product of Nihon Shokubai Co.) can be cited.
As another commercial dispersing agents, DEMOL EP (product of Kao Chemical Co.) that is polycarboxylate, VANILLEX N (product of Nihonseishi Co.) that is lignin sulfonate, VISPERSE P-121 (product of Nihonseishi Co.) that is bisphenolsulfonate, or similar product can be employed.
In the present invention, as the dispersing agent, water-soluble acrylic resin and its derivatives are preferable to employ, in particular, ammonium salt or sodium salt of the water-soluble acrylic resin is preferable to employ. Further, compounding amount of the dispersing agent is preferable to be in the range of 0.05 to 25% by weight to manganese oxide or the solid solution of manganese oxide and ferric oxide. When the compounding amount of the dispersing agent to manganese oxide or the solid solution of manganese oxide and ferric oxide is less than 0.05% by weight, particles of manganese oxide or particles of the solid solution tend to coagulate. Further, when the compounding amount of the dispersing agent exceeds 25% by weight, in addition to coagulation of manganese oxide particles or particles of the solid solution, pin-holes tend to occur in the formed light absorption layer to result in a problem.
In the present invention, as solvent, water alone, or solvent mixture prepared by mixing water and an organic solvent compatible with water can be employed. Here, as an organic solvent compatible with water, alcohols such as methanol, ethanol, and propanol, glycols such as ethylene-glycol and propylene-glycol, glycol-ethers such as propylene glycol monomethyl ether and propylene glycol monoethyl ether, and polar solvents such as 2-pyrrolidone, N-methyl-pyrrolidone, dimethylformamide, and dimethyl sulfoxide can be employed.
Further, to the dispersion liquid composition of the present invention, methyl-polysiloxane or dimethyl-polysiloxane that is denatured by alkylene oxide such as ethylene oxide or propylene oxide may be added. By adding such polysiloxanes, coating property to glass panel can be improved, thereby a black layer having homogeneity and uniform thickness can be formed.
In the present invention, among the aforementioned denatured polysiloxanes, it is desirable to employ one that has HLB (hydrophile-lypophile balance) value from 3 to 18. When the HLB value is less than 3, since compatibility between water and polysiloxane is not sufficient, sufficient improvement effect of the coating property of the dispersion liquid can not be obtained. Further, when the HLB value exceeds 18, foam occurs in the dispersion liquid to cause inhomogeneity in the coated layer.
As commercial denatured polysiloxanes to be added to improve the coating property, there are, for example, SILWET L-7001, Fz-7064, Fz-2165 (all of them are products of Nihonunicar Co.). Further, polyvinyl alcohol can be employed. Polyvinyl alcohol is preferable to employ, when the solid solution of manganese oxide and ferric oxide is employed.
Further, addition amount of such additives to the total of the dispersion liquid is desirable to be in the range of 0.05 to 0.5% by weight. When the addition amount is less than 0.05% by weight, the dispersion liquid is repelled by the panel such as glass or similar, accordingly there tends to occur spot like non-coated portions 5 (illustrated in FIG. 4A) in the light absorption layer 2. On the contrary, when the addition amount exceeds 0.5% by weight, the layer thickness of the light absorption layer 2 becomes non-uniform and there tends to appear steps 6 (illustrated in FIG. 4B) running radially from center portion to periphery portion. Therefore, in any cases, uniformity of image is deteriorated.
As the display device of the present invention, a color cathode ray tube, a field emission display (FED), a plasma display panel (PDP) or similar device can be cited.
The structures of these display devices will be described with reference to drawings.
A color cathode ray tube, as shown in FIG. 5, has an external envelope comprising a glass panel 7, that is a transparent panel, a funnel 8 and a neck 9. On an interior surface of the panel 7, there is disposed a phosphor screen 10 that will be described later, and further inside thereof, a shadow mask 11 is disposed opposed to the phosphor screen 10. On the other hand, inside the neck 9 of the external envelope, electron guns 13 that emit electron beams 12 are disposed. In addition, inside of the funnel 8, there is disposed an inner shield 14 for shielding the electron beams from an external magnetic field. Outside of the funnel 8, there is disposed a deflection device 15 for deflecting the electron beams 12 by a magnetic field generated thereby.
The phosphor screen 10, as shown in FIG. 6A and FIG. 6B, is constituted of a light absorption layer 16 formed in matrix formation, and phosphor layers 17B, 17G and 17R of respective colors of blue, green, and red arranged and formed regularly in holes of prescribed shape (for example, in circular dot formation) in the light absorption layer 16. The light absorption layer 16 includes manganese oxide of an average particle diameter of 50 to 2000 nm, or the solid solution of manganese oxide and ferric oxide of which average particle diameter is 50 to 2000 nm and of which manganese content is 15 to 70% by weight. In order to enhance color purity, between the phosphor layers 17 and the panel 7, optical filters corresponding to emission colors of the respective phosphor layers 17 may be interposed.
The phosphor screen 10 of such a color cathode ray tube can be manufactured through, for example, the following respective steps shown from FIG. 7A to FIG. 7G.
First, as shown in FIG. 7A, a photo-resist layer 18, after formed on the interior surface of a glass panel 7, is exposed through a shadow mask 11 and is hardened with a pattern corresponding to electron beam going through holes 11a of the shadow mask 11. Next, the photo-resist layer is developed and dried to let remain photo-cured layer 19 of dot shape at positions destined to form the phosphor layers (FIG. 7B).
Next, over the whole interior surface of the panel 7 thereon the photo-cured layer 19 is formed, the aforementioned dispersion liquid composition of the present invention is coated and dried to form a bound layer 20 of manganese oxide or solid solution of manganese oxide and ferric oxide, both of which are light absorption material (FIG. 7C). Thereafter, the photo-cured layer 19 is dissolved and peeled by a decomposing agent such as sulfamic acid and hydrogen peroxide water, thereby the bound layer 20 of the light absorption substance formed thereon is removed. Thereby, holes destined to form the phosphor layer are exposed. Thereby, the light absorption layer 16 with a prescribed pattern is formed (FIG. 7D).
Thereafter, on the interior surface of the panel 7 thereon the light absorption layer 16 is formed in matrix, a blue phosphor layer 17B, a green phosphor layer 17G, and a red phosphor layer 17R are formed in turn by a slurry method, respectively. In the slurry method, on the light absorption layer 16, a blue phosphor slurry, for example, is coated and dried to form a film 21 of the blue emitting phosphor over all the interior surface of the panel 7. Here, the blue phosphor slurry contains a blue emitting phosphor (ZnS: Ag, Al) and PVA (polyvinyl alcohol) and dichromate as its main components, and is added a surfactant. To this film 21 of the blue emitting phosphor, ultra-violet light is irradiated through the shadow mask 11 (FIG. 7E). The film 21, after exposed thus, is developed and followed by removal of non-cured portion by cleaning. Thereby, the blue phosphor layer 17B of dot shape is formed at the prescribed positions (FIG. 7F).
Following this, as identical as the blue phosphor layer 17B, the green phosphor layer 17G and the red phosphor layer 17R are formed sequentially. Thereby, on the interior surface of the panel 7, a light absorption layer 16 formed in matrix formation and a phosphor screen 10 comprising of blue phosphor layer 17B, green phosphor layer 17G, and red phosphor layer 17R all of which are formed in dots, are formed (FIG. 7G). Here, the green phosphor slurry contains a green emitting phosphor (ZnS: Cu, Al) and PVA (polyvinyl alcohol) and dichromate as its main components, and is added a surfactant. The red phosphor slurry contains a red emitting phosphor (Y2O2S:Eu) and PVA (polyvinyl alcohol) and dichromate as its main components, and is added a surfactant.
Next, as other examples of the display device of the present invention, the structure of a field emission display (FED) and a plasma display panel (PDP) will be described.
In the FED, as shown in FIG. 8, a substrate 21 of an electron emitting side and a substrate 22 of a light emitting side are disposed opposed each other in parallel to form a vacuum envelope. At the substrate 21 of the electron emitting side, on a silicon substrate 23, a film of silicon dioxide 25 having quite a many cavities 24 is formed. On this film of silicon dioxide 25, gate electrodes 26 consisting of Mo or Nb are formed, and on the silicon substrate 23 inside of the cavities 24, conic electron emitting elements 27 consisting of Mo are formed.
Further, at the substrate 22 of the light emitting side, on a surface of a transparent glass substrate 28 opposed to the electron emitting elements 27, a phosphor screen 10 is formed. The phosphor screen 10 comprises, as shown in FIG. 9, a light absorption layer 16 formed in matrix, and a phosphor layer 17 of blue emitting, green emitting, and red emitting phosphors arranged and formed regularly in holes of prescribed shape of the light absorption layer 16. The light absorption layer 16 contains, as the light absorption substance, manganese oxide of an average particle diameter of 50 to 2000 nm, or solid solution of manganese oxide and ferric oxide of which average particle diameter is in the range of 50 to 2000 nm and of which manganese content is in the range of 15 to 70% by weight. Further, to support the load on the silicon substrate 23 added by weight of the phosphor screen 10 and the glass substrate 28 and atmospheric pressure, there is disposed a supporting member 29 between the substrate 21 of the electron emitting side and the substrate 22 of the light emitting side.
In this display device, electron beams emitted from many of the electron emitting elements 27 are irradiated on the phosphor screen 10, thereby the respective phosphor layers 17 of the phosphor screen 10 emit light to display images. This phosphor screen 10 (the light absorption layer 16 and the respective phosphor layers 17) of the FED is also manufactured in an identical manner as, for example, that of the aforementioned phosphor screen of the color cathode ray tube.
Further, in an AC type PDP that is a third example of the display device of the present invention, as shown in FIG. 10, two glass substrates 30 and 31 of the rear side and the front side are disposed in parallel and opposed each other. They are supported a certain distance apart by a plurality of cell walls 32 disposed in parallel each other on the rear side glass substrate 30.
On the rear surface of the glass substrate 31 of the front side, a light absorption layer 16, and a composite electrode 35 constituted of a transparent electrode 33, that is a supporting electrode, and a metallic electrode 34, that is a bus electrode, are formed in parallel each other. In addition, covering the composite electrode 35, a dielectric substance layer 36 is formed, and further thereon a protective layer (MgO layer) 37 is formed.
On the other hand, on the front surface of the glass substrate 30 of the rear side, to be orthogonal with the composite electrodes 35, address electrodes 38 are formed located between the cell walls 32. Further, so as to cover over the address electrodes 38, the phosphor layer 17 is disposed.
In manufacturing a PDP having such a structure, on the glass substrate 31 of the front side, as identical way as that of the aforementioned color cathode ray tube, a light absorption layer 16 can be formed. In addition, formation of the phosphor layer on the glass substrate 30 of the rear side also can be performed as identical as the formation of the phosphor layer of the aforementioned color cathode ray tube.